A common parasite can increase a women's attractiveness to the opposite sex but also make men more stupid, an Australian researcher says.

About 40 per cent of the world's population is infected with Toxoplasma gondii, including about eight million Australians and perhaps 60 million Americans.

Human infection generally occurs when people eat raw or undercooked meat that has cysts containing the parasite, or accidentally ingest some of the parasite's eggs excreted by an infected cat.

The parasite is known to be dangerous to pregnant women as it can cause disability or abortion of the unborn child, and can also kill people whose immune systems are weakened.

Until recently it was thought to be an insignificant disease in healthy people, Sydney University of Technology infectious disease researcher Nicky Boulter said, but new research has revealed its mind-altering properties.

"Interestingly, the effect of infection is different between men and women," Dr Boulter writes in the latest issue of Australasian Science magazine.

"Infected men have lower IQs, achieve a lower level of education and have shorter attention spans. They are also more likely to break rules and take risks, be more independent, more anti-social, suspicious, jealous and morose, and are deemed less attractive to women.

"On the other hand, infected women tend to be more outgoing, friendly, more promiscuous, and are considered more attractive to men compared with non-infected controls.

"In short, it can make men behave like alley cats and women behave like sex kittens".

Dr Boulter said the recent Czech Republic research was not conclusive, but was backed up by animal studies that found infection also changes the behaviour of mice. The mice were more likely to take risks that increased their chance of being eaten by cats, which would allow the parasite to continue its life cycle.Rodents treated with drugs that killed the parasites reversed their behaviour, Dr Boulter said.

Another study showed people who were infected but not showing symptoms were 2.7 times more likely than uninfected people to be involved in a car accident as a driver or pedestrian, while other research has linked the parasite to higher incidences of schizophrenia.

"The increasing body of evidence connecting Toxoplasma infection with changes in personality and mental state, combined with the extremely high incidence of human infection in both developing and developed countries, warrants increased government funding and research, in particular to find safe and effective treatments or vaccines," Dr Boulter said.

What is toxoplasmosis?

A single-celled parasite called Toxoplasma gondii causes a disease known as toxoplasmosis. While the parasite is found throughout the world, more than 60 million people in the United States may be infected with the Toxoplasma parasite. Of those who are infected, very few have physical symptoms because a healthy person's immune system usually keeps the parasite at bay; however, it now appears that even a covert infection can result in mental and behavioral changes that can be just as devastating. For pregnant women and individuals who have compromised immune systems should be cautious; for them, a Toxoplasma infection could cause abortions, brain damage or death.

How do people get toxoplasmosis?

A Toxoplasma infection occurs by accidentally swallowing cat feces from a Toxoplasma-infected cat that is shedding the organism in its feces. This might happen if you were to accidentally touch your hands to your mouth after gardening, cleaning a cat's litter box, or touching anything that has come into contact with cat feces. Eating contaminated raw or partly cooked meat, especially pork, lamb, or venison or by touching your hands to your mouth after handling undercooked meat. It is also possible to become infected from knives, utensils, cutting boards and other foods that have had contact with raw, infected meat.

In some areas of the world it is possible that drinking water is contaminated with Toxoplasma.

What are the physical symptoms of toxoplasmosis?

Symptoms of the infection vary. Most people who become infected with Toxoplasma are not aware of it. Some people who have toxoplasmosis may feel as if they have the "flu" with swollen lymph glands or muscle aches and pains that last for a month or more.

above: T. gondii: T.gondii encephalitis (TE) is the most common cerebral opportunistic infection in patients with AIDS. The typical lesion is an ipodense focal area with ring contrast-enhancement and edema.(CT scan of a toxoplasmic encephalitis).

In severe toxoplasmosis damage to the brain, eyes, or other organs, can develop from an acute Toxoplasma infection or one that had occurred earlier in life and is now reactivated. Severe cases are more likely in individuals who have weak immune systems, though occasionally, even persons with healthy immune systems may experience eye damage from toxoplasmosis.

Most infants who are infected while still in the womb have no symptoms at birth, but they may develop symptoms later in life. A small percentage of infected newborns have serious eye or brain damage at birth.

Who is at risk for developing severe toxoplasmosis?

People who are most likely to develop severe toxoplasmosis include infants born to mothers who became infected with Toxoplasma for the first time during or just before pregnancy and also persons with severely weakened immune systems, such as individuals with HIV/AIDS, those taking certain types of chemotherapy, and those who have recently received an organ transplant.

What should I do if I think I am at risk for severe toxoplasmosis?

If you are planning to become pregnant, your health care provider may test you for Toxoplasma. If the test is positive it means you have already been infected sometime in your life. There usually is little need to worry about passing the infection to your baby. If the test is negative, take necessary precautions to avoid infection.

If you are already pregnant, you and your health care provider should discuss your risk for toxoplasmosis. Your health care provider may order a blood sample for testing.

If you have a weakened immune system, ask your doctor about having your blood tested for Toxoplasma. If your test is positive, your doctor can tell you if and when you need to take medicine to prevent the infection from reactivating. If your test is negative, it means you have never been infected and you need to take precautions to avoid infection.

What should I do if I think I may have toxoplasmosis?

If you suspect that you may have toxoplasmosis, talk to your health care provider. Your provider may order one or more varieties of blood tests specific for toxoplasmosis. The results from the different tests can help your provider determine if you have a Toxoplasma infection and whether it is a recent (acute) infection.

What is the treatment for toxoplasmosis?

Once a diagnosis of toxoplasmosis is confirmed, you and your health care provider can discuss whether treatment is necessary. In an otherwise healthy person who is not pregnant, treatment usually is not needed. If symptoms occur, they typically go away within a few weeks to months. For pregnant women or persons who have weakened immune systems, this parasite can be treated with sulfadiazine and pyrimethamine or clindamycin.

How can I prevent toxoplasmosis?

There are several general sanitation and food safety steps you can take to reduce your chances of becoming infected with Toxoplasma.

Wearing gloves when you garden or do anything outdoors that involves handling soil. Cats, which may pass the parasite in their feces, often use gardens and sandboxes as litter boxes. Wash your hands well with soap and water after outdoor activities, especially before you eat or prepare any food.

When preparing raw meat, wash any cutting boards, sinks, knives, and other utensils that might have touched the raw meat thoroughly with soap and hot water to avoid cross-contaminating other foods. Wash your hands well with soap and water after handling raw meat.

Cook all meat thoroughly; that is, to an internal temperature of 160 F and until it is no longer pink in the center or until the juices become colorless. Do not taste meat before it is fully cooked.

If I am at risk, would I be able to keep my cat?

Yes, you may keep your cat if you are a person at risk for a severe infection (e.g., you have a weakened immune system or are pregnant); however, there are several safety precautions to avoid being exposed to Toxoplasma:

Keep your cat healthy and help prevent it from becoming infected with Toxoplasma. Keep your cat indoors and feed it dry or canned cat food rather than allowing it to have access to wild birds and rodents or to food scraps. A cat can become infected by eating infected prey or by eating raw or undercooked meat infected with the parasite. Do not bring a new cat into your house that might have spent time out of doors or might have been fed raw meat. Avoid stray cats and kittens and the area they have adopted as their "home." Your veterinarian can answer any other questions you may have regarding your cat and risk for toxoplasmosis.

Have someone who is healthy and not pregnant change your cat's litter box daily. If this is not possible, wear gloves and clean the litter box every day, because the parasite found in cat feces needs one or more days after being passed to become infectious. Wash your hands well with soap and water afterwards.

Once infected with Toxoplasma is my cat always able to spread the infection to me?

No, cats only spread Toxoplasma in their feces for a few weeks following infection with the parasite. Like humans, cats rarely have symptoms when first infected, so most people do not know if their cat has been infected. The infection will go away on its own; therefore it does not help to have your cat or your cat's feces tested for Toxoplasma.